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Questions and Answers
What is the primary function of the SA node in the heart?
What is the primary function of the SA node in the heart?
- To collect oxygenated blood from the lungs
- To regulate blood pressure in the arteries
- To serve as the natural pacemaker (correct)
- To conduct electrical signals to the ventricles
Which type of cardiac action potential is associated with the SA and AV nodes?
Which type of cardiac action potential is associated with the SA and AV nodes?
- Cardiac mechanical potential
- Skeletal muscle potential
- Slow action potential (correct)
- Fast action potential
What is the approximate rate of impulses generated by the AV node?
What is the approximate rate of impulses generated by the AV node?
- 60-80 beats/minute
- 20-40 beats/minute
- 80-100 beats/minute
- 40-60 beats/minute (correct)
Where is the SA node located within the heart?
Where is the SA node located within the heart?
What mechanism causes ions to move across the membrane during the rapid action potential phase?
What mechanism causes ions to move across the membrane during the rapid action potential phase?
What membrane potential is needed for the sodium channels to close after depolarization?
What membrane potential is needed for the sodium channels to close after depolarization?
What is the primary role of the sodium channels with high threshold for opening?
What is the primary role of the sodium channels with high threshold for opening?
What characterizes the state changes of voltage-gated sodium channels?
What characterizes the state changes of voltage-gated sodium channels?
What is required for the fast action potential of the ventricles to be generated?
What is required for the fast action potential of the ventricles to be generated?
What could happen if the sodium channels do not reactivate properly after repolarization?
What could happen if the sodium channels do not reactivate properly after repolarization?
Which statement best describes the opening of sodium channels during depolarization?
Which statement best describes the opening of sodium channels during depolarization?
What is the importance of returning to the resting membrane potential of -90 mV?
What is the importance of returning to the resting membrane potential of -90 mV?
Which describes the nature of the stimulus intensity for opening fast sodium channels?
Which describes the nature of the stimulus intensity for opening fast sodium channels?
What is the primary effect of increased parasympathetic activity on automaticity?
What is the primary effect of increased parasympathetic activity on automaticity?
What is the total delay in conduction from the SA node to the ventricular muscle?
What is the total delay in conduction from the SA node to the ventricular muscle?
What physiological change occurs during the delay of conduction at the AV node?
What physiological change occurs during the delay of conduction at the AV node?
Which of the following conditions decreases automaticity?
Which of the following conditions decreases automaticity?
What is the significance of the slow rise in resting membrane potential (RMP) before reaching threshold potential?
What is the significance of the slow rise in resting membrane potential (RMP) before reaching threshold potential?
What occurs when the resting membrane potential is depolarized to the threshold potential?
What occurs when the resting membrane potential is depolarized to the threshold potential?
What is the resting membrane potential of the myocyte as described?
What is the resting membrane potential of the myocyte as described?
Which gate is closed at the resting stage of the sodium channels?
Which gate is closed at the resting stage of the sodium channels?
What initiates the opening of the fast voltage-gated sodium channels?
What initiates the opening of the fast voltage-gated sodium channels?
During which phase do the sodium channels remain unresponsive to any stimulus?
During which phase do the sodium channels remain unresponsive to any stimulus?
What happens to the H gate of the sodium channels during the resting phase?
What happens to the H gate of the sodium channels during the resting phase?
What configuration change occurs in sodium channels upon reaching the threshold potential?
What configuration change occurs in sodium channels upon reaching the threshold potential?
Which statement best describes the behavior of the sodium channels at resting membrane potential?
Which statement best describes the behavior of the sodium channels at resting membrane potential?
What triggers the activation of L-type calcium channels in pacemaker cells?
What triggers the activation of L-type calcium channels in pacemaker cells?
Which of the following statements is true regarding the resting membrane potential (RMP) of pacemaker cells?
Which of the following statements is true regarding the resting membrane potential (RMP) of pacemaker cells?
What is the primary mechanism behind the self-excitation of sinus nodal fibers?
What is the primary mechanism behind the self-excitation of sinus nodal fibers?
What characterizes the action potential generation in pacemaker cells?
What characterizes the action potential generation in pacemaker cells?
Which feature is specifically associated with the automaticity of cardiac cells?
Which feature is specifically associated with the automaticity of cardiac cells?
What ionic event occurs during phase 4 diastolic depolarization in pacemaker cells?
What ionic event occurs during phase 4 diastolic depolarization in pacemaker cells?
What is the effect of a high sodium concentration in the extracellular fluid (ECF) on pacemaker cells?
What is the effect of a high sodium concentration in the extracellular fluid (ECF) on pacemaker cells?
What is the significance of the threshold voltage of -40 mV in pacemaker cells?
What is the significance of the threshold voltage of -40 mV in pacemaker cells?
Study Notes
Types of Cardiac Cells
- SA node functions as the natural pacemaker of the heart, initiating impulses at a rate of 60-80 beats per minute.
- AV node acts as a secondary pacemaker with a slower rate of 40-60 beats per minute.
Types of Action Potentials
- Fast action potentials occur in the atria, ventricles, and Purkinje fibers.
- Slow action potentials are characteristic of SA and AV nodes.
SA Node Anatomy
- Measures about 3 mm wide, 15 mm long, and 1 mm thick, located in the right atrium near the superior vena cava.
Fast Action Potential Mechanism
- Involves rapid influx of sodium ions (Na⁺) through fast voltage-gated sodium channels after depolarization from -90 mV to approximately -65 mV.
- Sodium channels transition through three states: closed (resting), open (activation), and inactivated.
- Absolute refractory period occurs during phase 0 until partway through phase 1; no stimulus can activate channels during this time, necessitating higher thresholds for firing.
Ionic Basis for Fast Action Potential
- Sodium ions move across the membrane down their concentration and electrical gradients.
- L-type calcium channels activate when the membrane potential reaches about -40 mV, contributing to action potential generation.
Automaticity of Pacemaker Cells
- Pacemaker cells can generate spontaneous action potentials without external stimuli, a trait particularly developed in the SA and AV nodes.
- Automaticity results from leaky sodium and calcium channels leading to gradual depolarization.
Resting Membrane Potential (RMP)
- RMP for pacemaker cells is around -55 to -60 mV, with a threshold for action potential generation at about -40 mV.
Conditions Affecting Automaticity
- Increased parasympathetic activity (e.g., vagal stimulation) can decrease automaticity by negatively affecting phase 4 depolarization slope.
- Hyperoxemia may also influence automaticity.
Delay in Conduction Pathway
- Conduction time from the AV node to ventricular muscles is approximately 0.04 seconds, contributing to a total AV nodal delay of about 0.09 seconds.
- The total conduction time from the SA node to ventricular muscle is around 0.16 seconds, allowing time for atrial blood to empty into the ventricles before contraction.
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Description
Explore the different types of cardiac cells, including the SA and AV nodes, and their role in heart rhythm. This quiz will help you understand the variation in action potentials within the heart's chambers and conduction system. Test your knowledge of cardiac physiology.
